What's the Name of That Book??? discussion

I read this book possibly around 2006 and I think it was a fairly recent release (maybe 2004/5)
I think it could have been based in England where a single mother relocates her three kids to a farm and at first the kids hate it. But then they meet a boy from next door and there’s a hole in the hedge which is how they sneak out to go on adventures. A horse and cart also feature.
The cover is a dark blue and yellow from memory and has the silhouettes of the kids on the left in the blue, and potentially also had the horse too. I think the title was kind of long which is why I can’t remember it

I stupidly gave this book away many years ago and would love to find it again - any clues will be a great help!

A lot of this sounds like The Penderwicks: A Summer Tale of Four Sisters, Two Rabbits, and a Very Interesting Boy particularly the cover description and there is also a hole in the hedge and meeting the boy next door. However, it is a single father, not mother, and there are four sisters, not three. Still, the oldest sister is very much a mother figure and the tone of the book is memorable and could make you think it might be based in England and it was first published in 2005.

There is also a cover where the blue is darker:

oh my goodness I think it is!! Thank you so much!

You're very welcome. :)